1. Field of the Invention
The present invention relates mainly to a carburetor control system for a general-purpose engine, and relates especially to an improvement of a carburetor control system comprising: a governor device coupled to a throttle lever for opening and closing a throttle valve, the governor device opening the throttle valve when an operation of an engine is stopped, the governor device opening or closing the throttle valve in accordance with a rotational number of the engine when the engine is in operation; a choke return spring urging a choke lever for opening and closing a choke valve in a direction to close the choke valve; and an automatic choke device connected to the choke lever to open the choke valve in accordance with an increase in temperature of the engine.
2. Description of the Related Art
Such a carburetor throttle valve control system has already been known as disclosed in for example Japanese Patent Application Laid-open No. 2006-242143.
In such a conventional carburetor control system, the choke valve is controlled to a fully closed state by the automatic choke device when the engine is in a cold idling state. In addition, the carburetor is generally provided with a relief mechanism that opens the choke valve in accordance with an increase in the intake negative pressure generated downstream of the choke valve when the intake negative pressure reaches a predetermined value or more. Here, in the relief mechanism, it is desired that a set load of a relief spring is set as small as possible in order to facilitate the opening of the choke valve with the intake negative pressure, thereby preventing an excessive injection of fuel during cold idling of the engine. However, since the pulsation of the intake negative pressure is relatively strong when the engine is in an idling state, if the set load is set sufficiently small, the degree of opening of the choke valve becomes unstable due to the pulsation of the intake negative pressure. This being the situation, the reality is that the set load of the relief spring cannot be set sufficiently small. In this point, there is a room for improvement of the fuel efficiency of the engine.